Small NRD guide bend

ABSTRACT

An LSE mode, which is a parasitic mode, can be effectively suppressed by a simple structure, and a reduction in size and weight can be thereby facilitated. Further, a metal body  3  is arranged in the vicinity of a dielectric waveguide  1  of an NRD guide to suppress the LSE mode, the NRD guide being configured to propagate electromagnetic waves through the dielectric waveguide  1  which is sandwiched between parallel conductor plates with a gap of less than a ½ wavelength. This metal body  3  has an arbitrary shape, and may have a discoid shape, an elliptic shape or a prismatic shape. Furthermore, an even distance d is maintained between the metal body  3  and the dielectric waveguide  1 , and a phase constant difference can be suppressed by changing this distance d.

TECHNICAL FIELD

The present invention relates to an NRD guide bend capable oftransferring with suppression of an electromagnetic field of an LSE modewhich is a parasitic mode in an NRD guide (Nonradiative Dielectric WaveGuide) as an elemental technology realizingultrahigh-speed/high-capacity wireless communication, and moreparticularly to an NRD guide bend for a millimeter-wave band.

BACKGROUND ART

In recent years, there have been proposed a wide variety of broadbandcircuit elements each of which is available for the realization ofultrahigh-speed/high-capacity wireless communication device. Inparticular, development of a broadband circuit element which covers the59 to 66 GHz band is important. With this development, it is possible torealize an ultrahigh-speed wireless LAN, a home link, cable TV wirelesstransfer, an inter-vehicle communication system and other applicationsat a transmission rate exceeding, e.g., 400 Mbps.

As such a millimeter-wave or microwave transmission circuit, an NRDguide has been conventionally used (see JP-A-2000-341003). In this NRDguide, as shown in FIG. 17( a), a dielectric waveguide 101 formed of,e.g., Teflon® (registered trademark for polytetrafluoroethylene) having,e.g., a dielectric constant ∈r=2.04 is provided between a pair ofparallel conductor plates 102 a and 102 b. A width of each of theseconductor plates 102 a and 102 b, i.e., a height of the dielectricwaveguide 101 is set to be less than a ½ wavelength of a frequency of anelectromagnetic wave propagated through this dielectric waveguide 101,and a width of the dielectric waveguide 101 is set to be approximately a½ wavelength. For example, if an operating frequency is 60 GHz, a heightof the dielectric waveguide 101 is set to 2.25 mm and a width of thedielectric waveguide 101 is set to 2.5 mm. As a result, anelectromagnetic wave having the operating frequency can be propagatedthrough the dielectric waveguide 101, but the electromagnetic wavehaving the operating frequency cannot be propagated outside thedielectric waveguide 101 in a widthwise direction of the dielectricwaveguide 101, and hence the electromagnetic wave having the operatingfrequency is trapped in and transmitted through the dielectric waveguide101.

Although an electromagnetic field in a cross section is generated in anoperating mode (an LSM mode) of the electromagnetic wave having theoperating frequency transmitted through this dielectric waveguide 101 asshown in FIGS. 17( a) and 17(b), an LSE mode which is an unnecessaryparasitic mode is produced due to bending or branching of the dielectricwaveguide 101 as shown in FIG. 17( b).

In order to suppress this LSE mode, a mode suppressor 103 having a ¼wavelength choke configuration is inserted into the dielectric waveguide101 in the prior art as shown in FIG. 18.

SUMMARY OF THE INVENTION

In the producing process, the dielectric waveguide 101 is firstlydivided into two portions in a longitudinal direction. The portions ofthe dielectric waveguide 101 are then adhesively-connected to each otherafter the above-described conventional mode suppressor 103 is insertedbetween the portions of the dielectric waveguide 101. Theabove-described conventional mode suppressor encounters a problemresulting from the time-consuming and complicated producing process.

In view of the above-described problems, it is an object of the presentinvention to provide a small NRD guide bend (an NRD guide modesuppressor) which has a simple configuration and can effectivelysuppress an LSE mode which is a parasitic mode.

To this end, a small NRD guide bend according to claim 1 ischaracterized in that a conductor is arranged in the vicinity of adielectric waveguide of an NRD guide which propagates an electromagneticwave through the dielectric waveguide, the dielectric waveguide beingsandwiched between parallel conductor plates and having a gap which isless than a ½ wavelength.

According to the invention, it is possible to effectively suppress anLSE mode which is an unnecessary parasitic mode by simple externalarrangement, i.e., arranging the conductor in the vicinity of thedielectric waveguide of the NRD guide which transmits an electromagneticwave by using the dielectric waveguide which is sandwiched between theparallel conductor plates and has a gap which is less than a ½wavelength.

Further, in the above-described invention, the small NRD guide bend ischaracterized in that the conductor is a housing of an apparatusincluding the NRD guide.

Furthermore, in the above-described invention, the small NRD guide bendis characterized in that the conductor is provided in the vicinity of adirectional coupler formed of dielectric waveguides which are inproximity to each other and bent.

Moreover, in the above-described invention, the small NRD guide bend ischaracterized in that the conductors are provided along the dielectricwaveguide at equal intervals in proximity to each other, a curvatureradius of a bending portion of the dielectric waveguide is arbitrary,and an amplitude of the electromagnetic wave propagated through thedielectric waveguide is determined based on an angle of the bendingportion.

Additionally, in the above-described invention, the small NRD guide bendis characterized in that a distance between the dielectric waveguide andthe conductor is changed to adjust a phase constant difference of theelectromagnetic wave propagated through the dielectric waveguide.

Further, in the above-described invention, the small NRD guide bend ischaracterized in that a distance between the dielectric waveguide andthe conductor is approximately 0.5 mm.

Furthermore, in the above-described invention, the small NRD guide bendis characterized in that the conductor has a rod-like shape, and alength of the metal body is changed to vary a suppressed frequency of aparasitic mode generated in the dielectric waveguide.

Moreover, in the above-described invention, the small NRD guide bend ischaracterized in that the dielectric waveguide forms a bending portionof approximately 180 degrees, the conductor is provided on an inner sideof the bending portion, and a curvature radius of the conductor ischanged to vary a suppressed frequency of a parasitic bend generated inthe dielectric waveguide.

As described above, according to the present invention, it is possibleto demonstrate an advantage of enabling effective suppression of the LSEmode which is an unnecessary parasitic mode by using only a simpleexternal arrangement, i.e., arranging the conductor in the vicinity ofthe dielectric waveguide of the NRD guide which transmits anelectromagnetic wave through the dielectric waveguide which issandwiched between the parallel conductor plates and has a gap which isless than a ½ wavelength.

Additionally, according to the present invention, by providing theconductor as a housing of an apparatus including the NRD guide, effectsand advantages of both a housing function and a mode suppressingfunction can be obtained, thereby demonstrating an advantage offacilitating a reduction in size and weight.

Further, according to the present invention, by providing the conductorin the vicinity of a directional coupler formed by the dielectricwaveguides which are in proximity to each other and bent, a bendingradius of each bending portion can be reduced, whereby the directioncoupler which is small in size and weight can be advantageouslyobtained.

Furthermore, according to the present invention, conductors are providedat equal intervals along the dielectric waveguide in proximity to eachother, the bending portion of the dielectric waveguide has an arbitrarycurvature radius, and an amplitude of an electromagnetic wave propagatedthrough the dielectric waveguide is determined based on an angle of thebending portion, thereby advantageously assuredly reproducing the LSMmode.

Moreover, according to the present invention, since a phase constantdifference of an electromagnetic wave propagated through the dielectricwaveguide is adjusted by changing a distance between the dielectricwaveguide and the conductor, the bending portion having an arbitrarybending angle can be obtained, and an advantage of realizing theflexible NRD guide can be demonstrated.

Additionally, according to the present invention, a phase constantdifference of the NRD guide having a standard shape can be set to 0 bydetermining a distance between the dielectric waveguide and theconductor as approximately 0.5 mm, and the advantage of reproducing theLSM mode at an output port of a bend can be thereby obtained.

Further, according to the present invention, the conductor has arod-like shape, a suppressed frequency of the parasitic mode generatedin the dielectric waveguide is changed by varying a length of the metalbody, or the dielectric waveguide forms the bending portion ofapproximately 180 degrees, the conductor is provided on the inner sideof the bending portion, and a curvature radius of the conductor ischanged to vary the suppressed frequency of the parasitic mode generatedin the dielectric waveguide, thereby obtaining an advantage ofeffectively suppressing an operating frequency as a suppression target.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a configuration of an NRD guide modesuppressor which is Embodiment 1 according to the present invention;

FIG. 2 is a cross-sectional view of the NRD guide mode suppressordepicted in FIG. 1 taken along a line A-A;

FIG. 3 is a view showing an example of the NRD guide mode suppressordepicted in FIG. 1;

FIG. 4 is a view showing frequency dependence of an LSM mode and an LSEmode obtained by the NRD guide mode suppressor depicted in FIG. 3;

FIG. 5 is a view showing an experimental result of frequency dependenceof the LSM mode obtained by the NRD guide mode suppressor illustrated inFIG. 3 and an NRD guide having no metal body provided thereto;

FIG. 6 is a schematic view showing a configuration of the NRD guide modesuppressor having a specified length of a metal body, which is the NRDguide mode suppressor illustrated in FIG. 3;

FIG. 7 is a view showing frequency dependence of the LSE mode when alength of the metal body is specified as a parameter in the NRD guidemode suppressor depicted in FIG. 6;

FIG. 8 is a view showing an example of an NRD guide mode suppressor inwhich a housing also serves as a metal body;

FIG. 9 is a schematic view showing a configuration of an NRD guide modesuppressor as a 3-dB coupler which is an embodiment according to thepresent invention;

FIG. 10 is a view showing frequency dependence of transmissioncharacteristics in case of the NRD guide mode suppressor depicted inFIG. 9 and in case of a counterpart having no metal body providedthereto;

FIG. 11 is a view showing a dielectric wavguide forming part of the NDRguide mode suppressor according to the third embodiment of the presentinvention;

FIG. 12 is a view showing gap dependence of a dielectric waveguide and ametal body with respect to a phase constant difference;

FIG. 13 is a view showing an example of an NRD guide mode suppressorwhich realizes a unity coupling angle at which a phase constantdifference becomes zero;

FIG. 14 is a view showing another example of the NRD guide modesuppressor which realizes the unity coupling angle at which the phaseconstant difference becomes zero;

FIG. 15 is a schematic view showing a configuration of the NRD guidemode suppressor which is Embodiment 3 according to the presentinvention;

FIG. 16 is a view showing frequency dependence of the LSM mode and theLSE mode when a distance between the dielectric waveguide and the metalbody is specified as a parameter in the NRD guide bend suppressordepicted in FIG. 15;

FIG. 17 is a view showing electric field distributions of the LSM modeand the LSE mode; and

FIG. 18 is a perspective view showing a configuration of an NRD guideusing a conventional mode suppressor.

DESCRIPTION OF REFERENCE NUMERALS

-   1, 11, 21, 22, 31, 61 dielectric waveguide-   2 a, 2 b conductor plate-   3, 13, 23, 33, 43, 53, 63 metal body-   4 housing-   P1 to P4 port

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of an NRD guide mode suppressor according to thepresent invention will now be described in detail hereinafter withreference to the accompanying drawings.

EMBODIMENTS Embodiment 1

FIG. 1 is a schematic view showing a configuration of an NRD guide modesuppressor which is Embodiment 1 according to the present invention.Further, FIG. 2 is a cross-sectional view of the NRD guide modesuppressor depicted in FIG. 1 taken along a line A-A. In FIGS. 1 and 2,this NRD guide mode suppressor has a dielectric waveguide 1 sandwichedbetween parallel conductor plates 2 a and 2 b as shown in FIG. 2. Thedielectric waveguide 1 is realized by Teflon® (polytetrafluoroethylene)having a dielectric constant ∈r=2.04 and a loss tangent tan δ ofapproximately 1.5×10⁻⁴, and has a height a of 2.25 mm and a width b of2.5 mm as shown in FIG. 2. Assuming that an operating frequency of anelectromagnetic wave propagated through the dielectric waveguide 1 is 60GHz, its wavelength λ is 5 mm, the height a is less than λ/2, and hencethe electromagnetic wave having the operating frequency is notpropagated between the conductor plates 2 a and 2 b other than thedielectric waveguide 1. On the other hand, in the dielectric waveguide1, the wavelength λ is shortened, and the electromagnetic wave havingthe operating frequency can be propagated. As a result, in an operatingfrequency band, there is formed an NRD guide in which theelectromagnetic wave is propagated through the dielectric waveguide 1alone.

Here in FIG. 1, the dielectric waveguide 1 is configured to bend with acurvature radius R and, in this case, an electromagnetic wave in an LSEmode as a parasitic mode is generated besides an LSM mode which is theabove-described operating mode. Here in FIGS. 1 and 2, when a metal body3 as a conductor is provided in the vicinity of the dielectric waveguide1, the LSE mode is suppressed. A distance d (FIG. 1) between this metalbody 3 and the dielectric waveguide 1 may be zero, and anelectromagnetic wave in the LSE mode is effectively suppressed if thisdistance is approximately 0.5 mm when the operating frequency is in a 60GHz band. It is to be noted that the metal body 3 has an arbitrary shapeand, the LSE mode suppression effect can be obtained even if variouskinds of shapes such as a discoid shape, an elliptic shape, a prismaticshape and others are adopted.

FIG. 3 is a view showing a configuration of the NRD guide modesuppressor when the metal body 3 of FIGS. 1 and 2 is a rod-like metalbody 13. A dielectric waveguide 11 corresponding to the dielectricwaveguide 1 has a curvature radius R of 12 mm, a cross-sectional shapeand a material which are the same as those of the dielectric waveguide 1depicted in FIGS. 1 and 2. It is determined that the minimum distancebetween the metal body 13 and the dielectric waveguide 1 is a distanced. Furthermore, a cross-sectional shape of the metal body 13 is anH-like shape, and each side forming the H-like shape is λ/4.

FIG. 4 is view showing frequency dependence (GHz) of output levels(S₂₁[dB]) in the LSM mode and the LSE mode which are output from a portP2 which is the other end of the NRD guide mode suppressor depicted inFIG. 3 when an electromagnetic wave in the LSM mode is input from a portP1 which is one end of the NRD guide mode suppressor. Here, FIG. 4 showscases where R=12 mm and the distance d is 0.5 mm and where the distanced is infinite, i.e., ∞, where the metal body 13 is not provided. Asshown in FIG. 4, when the metal body 13 is not provided, an LSM modeoutput is lowered particularly in a low frequency band, and occurrenceof the LSE mode indicates a large value from −4 dB to −10 dB. On theother hand, when the metal body 13 is provided, the electromagnetic wavein the LSM mode input from the port P1 is output from the port P2without substantially changing its level, and the generated LSE mode issuppressed to −15 dB or below, and further suppressed to approximately−40 dB in the vicinity of the operating frequency which is 61 GHz.

Moreover, FIG. 5 shows an experimental result of the LSM mode outputwhich is output from the port P2 with respect to the LSM mode outputwhich is input from the port 1 in the configuration illustrated in FIG.3 where R=12 mm and the distance d is 0.5 mm and where the distance d isinfinite, i.e., ∞, where the metal body 13 is not provided. As shown inFIG. 5, although the dependence (S₂₁[dB]) on the frequency (GHz) havinga spike-like ripple is demonstrated when the metal body 13 is notprovided, the substantially fixed frequency dependence with extremelyreduced attenuations is demonstrated when the metal body 13 is providedand hence stable output characteristics can be obtained.

Here, when a length l of the metal body 13 in the NRD guide modesuppressor depicted in FIG. 3 is changed as shown in FIG. 6, an LSE modeoutput to be suppressed demonstrates such frequency dependence as shownin FIG. 7. FIG. 7 shows the dependence (S₂₁[dB]) on the frequency (GHz)where R=12 mm, d=0.5 mm at l=5.00 mm, 7.50 mm and 10.00 mm. That is,when the curvature radius R=12 mm and the distance d=0.5 mm of thedielectric waveguide 11 including ports P1 and P2 remain unchanged andthe length l of the metal body 13 is sequentially changed to 5.00 mm,7.50 mm and 10.0 mm, a minimal value of the LSE mode tends tosequentially shift to approximately 61.8 GHz, approximately 62.3 GHz andapproximately 63.7 GHz. Therefore, the NRD guide mode suppressor canexcellently suppress the LSE mode under the condition that the length 1of the metal body 13 is set in accordance with the minimal value of theLSE mode corresponding to the operating frequency.

It is to be noted that the effect of suppressing the LSE mode can beobtained even though the above-described metal body 3 has an arbitraryshape, and hence the LSE mode can be also suppressed by arranging ahousing 4 formed of a conductor which is a housing of the NRD guide tobe closer to the bending dielectric waveguide 1 like the metal body asshown in, e.g., FIG. 8., which shows the LSM and LSE mode of thedielectric waveguide 1 at radius R and distance d in the housing 4. Inthis case, the housing 4 demonstrates an original function of thehousing and a function of the metal body as a mode suppressor, therebyfacilitating a reduction in size and weight of the NRD guide.

Embodiment 2

Embodiment 2 according to the present invention will now be described.In Embodiment 1 mentioned above, the LSE mode is suppressed when thedielectric waveguide 1 of the NRD guide is generally bent, but the LSEmode is suppressed in the NRD guide serving as a 3-dB coupler in thisEmbodiment 2.

FIG. 9 is a schematic view showing a configuration of an NRD modesuppressor applied to a 3-dB coupler which is Embodiment 2 according tothe present invention. Referring to FIG. 9, in this 3-dB coupler,dielectric waveguides 21 and 22 having ends of curved semicircles on oneside being close to each other are provided, an electromagnetic wavehaving an operating frequency input from a port P1 at the other end ofthe dielectric waveguide 21 is subjected to 3 dB coupling between thedielectric waveguides 21 and 22 which are in proximity to each other,and the electromagnetic wave having the operating frequency is outputfrom a port P4 at the other end of the dielectric waveguide 22. Here,like Embodiment 1, when a metal body 23 corresponding to the metal body13 is arranged in proximity to the both dielectric waveguides 21 and 22,the LSE mode propagated through the dielectric waveguides 21 and 22 issuppressed like Embodiment 1.

FIG. 10 shows frequency dependence (S[db]) of reflection (S₁₁) atfrequency (GHz) at the port P1 and an output (S₂₁) at the port P4 whenthe metal body 23 is arranged and when the metal body 23 is notarranged. That is with a metal body and R=12 mm and without a metal bodyand R=22.65 mm for ports P1 and P4. Here, although substantially thesame frequency dependence is shown in both cases where the metal body 23is arranged and where the metal body 23 is not arranged, a curvatureradius R of each of the dielectric waveguides 21 and 22 is 12 mm whenthe metal body 23 is provided, whereas the curvature radius R of eachdielectric waveguide is changed to 22.65 mm when the metal body 23 isnot provided. That is, in case of acquiring transmission characteristicsof the same reflection and output, providing the metal body 23 canreduce a length to ½ and an area to approximately ¼.

The curvature radius R of each dielectric waveguide can be reduced inthis manner because the LSE mode generated at a bending portion issuppressed by provision of the metal body 23 as described above. As aresult, the miniaturized 3-dB coupler can be realized. In this case,when the metal body 23 is used for side walls of a housing likeEmbodiment 1, a reduction in size and weight of the 3-dB coupler can befurther facilitated.

Embodiment 3

Embodiment 3 according to the present invention will now be described.This Embodiment 3 realizes an NRD guide mode suppressor which cancompletely reproduce an input LSM mode while suppressing an LSE mode.

First, an operation principle of this Embodiment 3 will be explained.Considering such a dielectric waveguide 31 of an NRD guide as shown inFIG. 11, it is assumed that an electromagnetic wave having an operatingfrequency is input from a port P1 at one end of the dielectric waveguide31, propagated in the dielectric waveguide 31 and output from a port P2at the other end. Additionally, it is assumed that a curvature radius ofthis dielectric waveguide 31 is R, an angle from the port P1 to apredetermined position on the dielectric waveguide 31 is θ, and adistance from the port P1 to the predetermined distance on thedielectric waveguide 31 is z.

The electromagnetic waves input to the port P1 are propagated in a statewhere both the LSM mode and the LSE mode exist and, assuming that theelectromagnetic waves of the respective modes are a₁(z) and a₂(z),amplitudes |a₁(z)| and |a₂(z)| of the respective electromagnetic wavesin the LSM mode and the LSE mode can be represented as the followingexpressions (1) and (2)|a ₁(z)|=√(cos²(Γ·z/2)+(Δβ/Γ)²·sin²(Γ·z/2))   (1)|a ₂(z)|=(2·c/Γ)|sin(Γ·z/2)|  (2)whereΓ=√(4c ²+Δβ²)   (3)Here, z is a propagation length on a bend, c is a mode couplingcoefficient, and Δβ is a phase constant difference between the LSM modeand the LSE mode.

The following description is directed to the case that the dielectricwaveguide 31 made of Teflon® (polytetrafluoroethylene) and shown in FIG.12 has a width of 2.5 mm and a height of 2.25 mm. FIG. 12 shows thephase constant difference Δβ as a function of distance d (mm) at a sideand both sides of the metal body 33 and the dielectric waveguide 31. InFIG. 12, the character “d” is intended to indicate a distance betweenthe dielectric waveguide 31 and each metal body 33. From the calculationresult of the phase constant difference Δβ between the LSM mode and theLSE mode to the distance “d” shown in FIG. 12, it will be understoodthat the phase constant difference Δβ is reduced as the distance d isincreased. Here, a remarkable point is that the phase constantdifference Δβ becomes zero when the distance d is 0.5 mm. At this time,the above-described expressions (1) and (2) become simple expressionsrepresented as the following expressions (4) and (5).|a ₁(z)|=|cos(c·z)|  (4)|a ₂(z)|=|sin(c·z)|  (5)Here, since it is theoretically known that the mode coupling coefficientc is in inverse proportion to the curvature radius R and the distance zis in proportion to the curvature radius R, the following expressions(6) and (7) can be obtained.c=c ₀ /R (c ₀: a constant)   (6)z=R·θ  (7)

Thus, when these expressions (6) and (7) are assigned in the expressions(4) and (5), the following expressions (8) and (9) can be obtained.|a ₁(z)|=|cos(c ₀·θ)|  (8)|a ₂(z)|=|sin(c ₀·θ)|  (9)

The same result can be also obtained by sandwiching the dielectricwaveguide 31 between the two metal bodies 33 as shown in a left-handinserted view of FIG. 12, Δβ in this example is as indicated by a brokenline in the same drawing, and a gap with which Δβ=0 can be achieved is0.8 mm.

Based on these expressions (8) and (9), the respective amplitudes of theLSM mode and the LSE mode do not concern the curvature radius R at all.That is, the curvature radius R does not relate to a design at all andcan be arbitrarily determined. That is, even if the dielectric waveguidehas any curvature radius, the LSM mode can be reproduced by providing agiven fixed angle, i.e., a unity coupling angle θo.

FIGS. 13 and 14 show examples of NRD guide mode suppressors having metalbodies 43 and 53 provided thereto in such a manner that the phaseconstant difference Δβ=0 can be achieved in the LSM mode for dielectricwaveguide 31, and a unity coupling angle θo is 195° in FIG. 13 whilst aunity coupling angle θo is 205° in FIG. 14. It is to be noted that FIG.13 shows an example where the metal body 43 is attached on the outerside of the dielectric waveguide 31 and FIG. 14 shows an example wherethe metal body 53 is attached on the inner side of the dielectricwaveguide 31. Incidentally, although a bending curvature exceeding 180°is consequently demonstrated in this case, it is good enough to changethe distance d to adjust the phase constant difference Δβ by using therelationship shown in each of FIG. 12 and finally effect optimizationwhen the NRD guide mode suppressor shown in FIGS. 13 and 14 is bent at180°. Further, the dielectric waveguide having an arbitrary bendingangle can be likewise optimized by changing the distance d to adjust thephase constant difference Δβ.

For example, it is possible to realize such an NRD guide mode suppressorhaving a bending angle of 180° as shown in FIG. 15, which shows adielectric waveguide 61 with ports P1 and P2 and a metal body 63. Thatis, a discoid metal body 63 having a radius r is provided on the innerside of a dielectric waveguide 61 which has an arbitrary curvatureradius R and bends at 180°, and a distance d between the metal body 63and the dielectric waveguide 61 can be changed by varying this radius r,thereby adjusting a phase constant difference Δβ. In FIG. 15, the LSMmode can be reproduced by setting the distance d to approximately 1 mm.It is to be noted that, when the metal body 63 is not provided, the LSEmode is produced, and hence utilization is impossible.

Furthermore, in this case, when the radius r is changed, consequentlythe distance d is changed as shown in FIG. 16, a frequency of a minimalvalue in the LSE mode can be shifted, thereby realizing an NRD guidemode suppressor capable of effectively suppressing the LSE mode. FIG. 16shows the dependence (S21[db]) as a function of frequency (GHz) forLSM→LSE and LSE→LSM modes at R=8, 5.85, 5.75 and 5.65 mm.

It is to be noted that the description has been given as to the metalbodies 3, 13, 23, 33, 43, 53, and 63 in Embodiments 1 to 3, but thepresent invention is not restricted thereto, and any conductor can beused.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to obtain anadvantage of effectively suppressing an LSE mode which is an unnecessaryparasitic mode by the simple external arrangement alone, i.e., arranginga conductor in the vicinity of a dielectric waveguide of an NRD guidewhich transmits an electromagnetic wave through the dielectric waveguidewhich is sandwiched between parallel conductor plates and has a gapwhich is less than a ½ wavelength.

Moreover, according to the present invention, when the conductor is ahousing of an apparatus including the NRD guide, effects and advantagesof both a housing function and a mode suppressing function can beobtained, thereby facilitating a reduction in size and weight.

Additionally, according to the present invention, when the conductor isprovided in the vicinity of a directional coupler formed of dielectricwaveguides which are in proximity to each other and bent, a bendingradius of a bending portion can be reduced, thereby obtaining thedirection coupler reduced in size and weight.

Further, according to the present invention, the conductors are providedalong the dielectric waveguide at equal intervals in proximity to eachother, a curvature radius of a bending portion of the dielectricwaveguide is arbitrary, and an amplitude of an electromagnetic wavepropagated through the dielectric waveguide is determined based on anangle of the bending portion, thereby obtaining an advantage ofassuredly reproducing an LSM mode.

Furthermore, according to the present invention, since a phase constantdifference of an electromagnetic wave propagated through the dielectricwaveguide is adjusted by changing a distance between the dielectricwaveguide and the conductor, a bending portion having an arbitrarybending angle can be acquired, thus obtaining an advantage of realizinga flexible NRD guide.

Moreover, according to the present invention, a phase constantdifference in an NRD guide having a standard shape can be set to zero bydetermining a distance between the dielectric waveguide and theconductor as approximately 0.5 mm, thereby obtaining an advantage ofreproducing an LSM bend at an output port of a bend.

Additionally, according to the present invention, the conductor has arod-like shape, a length of the metal body is changed to vary asuppressed frequency of a parasitic mode generated in the dielectricwaveguide, or the dielectric waveguide forms a bending portion ofapproximately 180 degrees, the conductor is provided on the inner sideof the bending portion, and a curvature radius of the conductor ischanged to vary a suppressed frequency of a parasitic mode generated inthe dielectric waveguide, thereby acquiring an advantage of effectivelysuppressing an operating frequency as a suppression target.

1. A small NRD guide bend, comprising: an NRD guide configured to allowelectromagnetic waves to propagate through a dielectric strip sandwichedbetween conducting plates parallel to each other, wherein a spacingbetween the conducting plates is less than half a wavelength of theelectromagnetic wave, and the dielectric strip is in a vicinity of ametal block.
 2. The small NRD guide bend according to claim 1, whereinthe metal block is a part of a housing for the NRD guide.
 3. The smallNRD guide bend according to claim 1, wherein the dielectric strip has acurved portion, the metal block has also a curved portion along thedielectric strip, a curvature radius of the metal block is adjusted tocontrol the resonant frequency of the parasitic mode to be suppressed inthe NRD guide.
 4. The small NRD guide bend according to claim 1, whereina gap between the dielectric strip and the metal block is approximately0.5 mm in width.
 5. The small NRD guide bend according to claim 1,wherein the metal block has a rectangular cross section, and a length ofthe metal block is adjusted to control the resonant frequency of theparasitic mode to be suppressed in the NRD guide.
 6. A small NRD guidebend, comprising: an NRD guide configured to allow electromagnetic wavesto propagate through a dielectric strip sandwiched between conductingplates parallel to each other, wherein a spacing between the conductingplates being less than half a wavelength of the electromagnetic wave,and the dielectric strip is in the vicinity of a couple of metal blocks.7. The small NRD guide bend according to claim 6, wherein gaps betweenthe dielectric strip and the metal blocks are adjusted to control thephase constant of the electromagnetic wave propagating through thedielectric strip.
 8. The small NRD guide bend according to claim 6,wherein a gap between one of the metal blocks and the dielectric stripis substantially equal to a gap between the other of the metal blocksand the dielectric strip in width.
 9. A small NRD guide bend,comprising: an NRD guide directional coupler constructed by a couple ofdielectric strips sandwiched between conducting plates parallel to eachother, wherein a spacing between the conducting plates is less than halfa wavelength of the electromagnetic wave, the dielectric strips are inthe vicinity of a metal block.